In an older design of a switch contact arrangement known from document DE 17 64 678 U, an erosion display is provided in which an erosion pointer held against a moving contact by spring pressure is free to move in a guide. The end extending beyond the guide represents a measure of the contact erosion. Additionally a metal sheet can be fitted and provided with indicator markings against which the extent of the erosion can be read off. The metal sheet is fastened to the switch housing by means of an elongated hole and screws to position it precisely at a point of origin. This positioning must be carried out with the switch housing open by making fine adjustments to the sheet metal indicator, which adds up to a considerable amount of work if there is a number of circuit-breakers in a switch installation.
In a further known switch contact arrangement for a low-voltage circuit-breaker, the erosion display comprises an erosion pointer and a display surface or display edge. The erosion pointer follows the movement of the first switch contact and, with the contacts closed, then extends beyond the display surface or display edge only when the value for the erosion of the switch contacts is less than a given maximum value (Instruction Manual for Circuit-Breaker 3WN6, Siemens AG, Germany, 1998). In this known switch contact arrangement, the moving switch contact has a contact holder and a plurality of contact levers supported on the contact holder by means of contact force springs. The metal erosion pointer is supported on one of the contact levers and located in a hole drilled in the contact holder in the direction of force of the contact force spring. A recess in the contact holder serves as an inspection hole, one side of which opens to the drill hole, such that the end of the erosion pointer facing away from the contact lever only extends into the inspection aperture when there is a permitted amount of erosion on contact surfaces formed on the contact levers(contact members). If the value for the erosion on these contact surfaces is greater than the predefined maximum value, the erosion pointer no longer extends into this inspection hole. This then indicates that the switch contact arrangement needs to be renewed. When the worn switch contacts have been replaced with new switch contacts, a new erosion pointer must be inserted into the drill hole on the contact holder and must then be shortened with the contacts closed so that after shortening, its end pointing away from the contact lever extends into the inspection hole by the value predefined for the maximum erosion, for example 2.7 mm. This shortening requires a special tool which can be inserted into the very narrow inspection hole. Since fitters regularly exchange worn switch contact arrangements on the premises of operators of such electrical switches, the fitters must be in possession of this special tool.
Based on a switch contact arrangement with features according to the preamble of the claims (Instruction Manual for Circuit-Breaker 3WN6, Siemens AG, Germany, 1998) the object of the invention is to design the erosion display in a way that makes shortening the erosion pointer easier.